Long story short, I can’t use multiple monitor RDP because I have different resolution monitors and they are stacked 2x2 instead of all in a row.
Did you try setting them up as one big display across all four, instead of four little ones? I think that’s something you can do.
Does the multi-mon RDP thing work from a Windows client too? I’d be surprised if it did, Windows’ multi-monitor support is fairly lacking in my experience too.